The present invention provides a method for preparing carbon tetrachloride from lower aliphatic hydrocarbons and/or their chlorinated or oxygenated derivatives; in particular the otherwise waste residues from industrial chemical processes such as, for example, the manufacture of vinyl chloride monomer, ethylene and propylene oxides and chloroprene. Such residues primarily contain saturated or unsaturated aliphatic substances, most often chlorinated, sometimes oxygenated, typically including dichloroethane, dichloropropane, dichloroisopropylether, the chlorobutenes, the chlorobutanes, and the like; possibly including also small proportions of cyclic derivatives, in particular aromatic substances.
Simply throwing away such residues presents a serious risk of pollution. Their treatment by combustion followed by a neutralization of the hydrogen chloride liberated, increases the cost price of the main products being manufactured. Ways have therefore been sought to upgrade the residues by various means of chlorination.
U.S. Pat. No. 3,676,508 discloses a two-step process for chlorinating mixtures of aromatic and aliphatic chlorides, but this process requires a pressure of 200 to 700 atmospheres at temperatures up to 800.degree. C. The product obtained is carbon tetrachloride. This process has the serious disadvantage of risking corrosion of the reactors, as well as the dangers of explosion and fire.
French Pat. No. 2,126,899 (see also British Pat. No. 1,316,709) proposes a process which likewise uses two steps of chlorination of essentially aliphatic chlorides. The first step takes place in the vapor phase at a temperature between 400.degree. and 600.degree. C., the second step takes place in liquid phase at a temperature between 100.degree. and 200.degree. C., in the presence of ferric chloride as catalyst. That process produces a mixture of carbon tetrachloride and perchloroethylene.